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GBB > Basics Of Genetics > Flashcards

Basics Of Genetics Flashcards

1
Q

Molecules of life

A
  • human body contains 100 trillion cells
  • nucleus in each cell (except blood cells)
  • each nucleus contains 46 chromosomes

-DNA is a stable source of information that is ably to replicate accurately and is capable of change

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2
Q

Search for molecular basis of heredity

A
  • search for genetic material:
    1. Griffiths transformation exp
    2. Averys transformation exp
    3. Hershey-chase bacteriophage exp
    4. Tobacco mosaic virus (TMV) exp
  • nucleotides: composition and structure
  • double helix model of DNA: Watson and crick
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3
Q

Timeline of events

A
  • 1890: Weismann- substance in the cell nuclei controls development
  • development of imaging equipment
  • 1900: chromosomes shown to contain hereditary information and composed of protein and nucleic acids
  • 1928: Griffiths transformation experiment
  • transfer of genetic information between cells through transformation
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4
Q

Griffiths Transformation exp

A
  • 1928
  • performed experiment on rats and 2 strains of bacteria that cause pneumonia
    • Type R (rough) = non-encapsulated, avirulent, relatively harmless
    • Type S (smooth) = encapsulated, virulent, severe pneumonia
  • combining living, non-virulent with heat-killed virulent causes rat to have bacteria/die
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5
Q

Averys Transformation

A
  • 1944
  • determined that the DNA from type S bacteria was the genetic material responsible for Griffiths results (not RNA)
  • adding S DNA to R bacteria produced S transformants
  • adding S RNA to R bacteria caused no S transformation
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6
Q

Hershey-Chase Bacteriophage ex

A
  • 1953
  • bacteriophage = a virus that attacks bacteria and replicated by invading a living cell and using cells molecular machinery
  • set up 2 replicates:
    1. Label DNA with phosphorus (32P)
    2. Label protein with sulfur (35S)
  • infected E. coli. With both types
  • 32P recovered and passed on to progeny
  • 35S no passed on to progeny
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7
Q

Grier & Schramm/Fraeknel-Conrad & Singer

Tobacco Mosaic Virus

A
  • 1956

- demonstrate the RNA is the genetic material of TMV

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8
Q

Early experiments summary

A
  1. Griffith (1928) and Avery (1944)
    • genetic transfer between cells; DNA is the transforming agent
  2. Hershey-Chase (1953)
    • DNA is the genetic material
  3. Gierer & Schramm… (1956)
    • RNA (not protein) is genetic material of some viruses
  4. Watson & Crick (1953)
    • double helix model of DNA
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9
Q

DNA and RNA

A

-formed from nucleotide polymers

  1. Penthouse sugar
    • DNA = deoxyribose
    • RNA = ribose
  2. Nitrogenous base
    • Purines = adenine, guanine
    • Pyrimidines = Ctyosone, Thymine, Uracil
  3. Phosphate group attached to 5’ carbon
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10
Q

Phosphodiester bond

A

-covenant bond between the phosphate group of one nucleotide and 3’ carbon of the sugar of another nucleotide

  • strong bond
  • DNA very stable
  • 5’ end = phosphate end
  • 3’ end = sugar
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11
Q

Watson & Crick

A
  • used base composition studies by Chargaff
    • double stranded DNA consists of 50% purines, 50% pyrimidines
    • %GC content varies between organisms
  • used X-ray diffraction studies by Franklin and Wilkins

-concluded that DNA is a helical structure with 0.34nm and 3.4 nm

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12
Q

Features of DNA model

A
  1. 2 polynucleotide chains wound in a right hand clockwise double helix
  2. Nucleotide chains are antiparallel (0.34nm apart)
  3. Sugar-phosphate backbone are on the outside of the double helix, bases oriented toward central axis
  4. Complementary base pairs from opposite strands bound together by weak H bond
    • A-T = 2 H bonds
    • C-G= 3 H bonds
  5. Base pairs are 0.34nm apart
    • one complete turn of helix requires 3.4nm/10 bases/turn
  6. Sugar-phosphate backbones are not equally spaced, resulting in major and minor grooves
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13
Q

DNA replication in cell nucleus

A
  • DNA unwinds and separates
  • each strand becomes template
  • base-pairs assembled on template by DNA-polymerase
  • nucleotides connected by DNA ligase
  • new DNA is semi conservative
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14
Q

RNA

A

-single stranded
-shorter than DNA
Less stable than DNA because of uracil
-5 carbon sugar is ribose
-function in transcription and translation

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15
Q

Regulation of gene expression in cells

A
  • DNA transcribed into mRNA which is then translated during protein synthesis
  • translation require tRNA and ribosomes
  • genetic code is a nonoverlapping triplet code
  • special sequence signal the initiation and termination of transcription and translation
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16
Q

Genophore

A
  • a chromosome without chromatic

- in prokaryotes

17
Q

Chromatin organization

A
  1. At the simplest level, chromatin is a double-helix structure of DNA
  2. DNA complexed with histones to form nucleosomes
  3. Each nucleosome consists of 8 histones. DNA wraps around 1.65 times
  4. Chromatosome consists of a nucleosome plus H1 histone
  5. The nucleosomes fold up to produce 30nm fibre
  6. Fibre forms loops averaging 300nm in length
  7. The 300nm fibres are compressed and folded to produce a 250nm wide fibre
  8. Tight coiling of 250nm fibre produces the chromatid of a chromosome
  • 100,000-fold shorter than its extended length
  • 146bp of DNA wrapped around a histone complex
18
Q

Chromatin condensation in cell cycle

A
  • during interphase 1 chromatin is least condensed
  • chromatin condensation begins during prophase 2
  • chromosomes remain condensed throughout stages 2-5 of mitosis
  • condensation and decondensation of chromatin changes during cell cycle through interactions with condensin and cohesin and mitotic spindle microtubules
  • condensation cooperates with biorientation os sister chromatids to segregate chromosomes
19
Q

Chromatin in cell

A
  • heterochromatin stays near the nuclear envelope
    • it is pushed to the outside as it is not transcribed and doesnt need to use transcription factors inside)
  • euchromatin congregates in the center and is transcriptionally active
20
Q

Heterochromatin

A
  1. Constitutive:
    • chromatin that is always heterochromatin in all cells at all times
    • telomeres, pericentromeres
  2. Facultative heterochromatin
    • chromatin that does not always need to be heterochromatin, but can convert to euchromatin when needed
    • X-chromosome in females are deactivated so that only one copy is active genes
21
Q

Centromeric DNA

A
  • (CEN)
  • centre of chromosome
  • specialized sequences function with the microtubules and spindle apparatus during mitosis/meiosis
22
Q

Telomeric DNA

A
  • at extreme ends of the chromosome
  • maintain stability
  • consist of tandem repeats
  • play a role in DNA replication and stability
  • disease arise from loss of telomeric DNA
  • a cell can only divide up to 250x due to shortening of telomeres
23
Q

Repeated DNA

A
  • may be interspaced or clustered
    1. SINEs: short interspaced repeated sequences (100-500bp)
    2. LINEs: long interspaced repeated sequences (>5000bp)
    3. Microsatellites: short tandem repeats (TTA,TTA,TTA)
  • repetitive elements constitute 45% of mammalian genome
24
Q

Transcription

A
  • DNA is copied into mRNA with aid of RNA polymerase

- RNA polymerase will bind to promoters that act as a signal in the DNA sequence to make RNA

25
Q

Control of gene expression

A
  • accomplished by controlling transcription initiation
  • regulatory proteins bind to DNA to either block or stimulate transcription depending on how they interact with RNA polymerase
  • eukaryotes regulate gene expression to maintain homeostasis
  • regulatory proteins gain access to bases in major grooves
    • regulatory proteins possess DNA-binding motifs
    • helix-turn-helix motif
    • homeodomain motif
    • zinc-finger motif
    • leucine zipper motif
26
Q

Factors of transcription regulation

A
  • DNA-binding transcriptions factors
  • chromatin regulators
  • coavtivators and corepressors: mediators
  • basal machinery: RNA pol II, GTF
27
Q

Main steps of transcription

A
  1. Polymerase binds to promoter sequences in helix (closed complex)
  2. Polymerase melts duplex near transcription start site - open complex
  3. Polymerase catalyzes phosphodiester linkage of 2 initial rNTPs
  4. Elongation: polymerase advances 3’-5’ down template melting duplex and adding rNTPs to growing rna
  5. Termination: at stop site, polymerase releases completed RNA and dissociated
28
Q

Transcription initiation steps

A
  1. Promoter start site recognition
  2. Promoter binding
  3. Promoter melting
  4. Transcription initiation
  5. Promoter escape/clearance
  6. Transcription elongation
29
Q

Stepwise recruitment of transcription factors

A
  • controlling expression of eukaryotic genes requires TFs
  • general TFs are required for transcription initiation (binding of RNA polymerase to DNA
  • specific TFs increase transcription in certain cells or in response to signals
  • ONLY when TFs bind to promoter that RNA polymerase is placed to allow initiation of transcription
30
Q

Eukaryotic gene transcription

A
  • coactivators and mediators are also required for the function of transcription factors
    • they bind to transcription factors and bind to other parts of transcription apparatus

-chromatin modifying proteins open up nucleosome structure to unwind DNA for RNA polymerase

31
Q

Mutations

A
  • mutations in regulatory sequence affect amount of transcription
    • possibly could creat a start site in wrong place to activate wrong gene
  • mutations in structural region affects the product function/size etc
    • affects mRNA and protein
32
Q

Mutation in an exon sequnce

A
  • prevention of transcription
  • prevention or incorrect processing of mRNA
  • protein with reduced/absent function or different function
33
Q

Point mutations

A
  • single base substitution
    • silent: substituted nucleotide codes for same AA
    • nonsense: incorrectly codes for STOP
    • missense: codes for wrong AA
34
Q

Frame-shift mutations

A
  • modification of reading frame after a deletion or insertion
  • all codons downstream affected
35
Q

PKU

A
  • phenylketonuria
  • insertion of premature stop codon (nonsense)
  • autosomal recessive
  • 1/12,000 newborns
  • genes not expressed to make phenylalanine hydroxase
  • cannot convert phenylalanine to tyrosine, which is precursor for dopamine and NE
  • can cause toxic build up in the body
  • treated with modified diet low in Phe
36
Q

Chromatin remodelling

A
  • addition of acetyl groups to histone tails remodel it to become accessible for transcription
  • acetyl groups neutralize the charge causing DNA to unwrap from histone and more accessible for TFs
  • Swi/Snf complex removes nucleosomes and deposits histone variants for specialized functions (heterochromatin
37
Q

Histones

A
  • highly conserved genes
  • high proportion of positively charged AAs (arginine and lysine) that facilitate binding negatively charged (acidic) DNA
  • form octomer
  • chromatin only found in eukaryotic cells
  • prokaryotes have genophore

GBB (9 decks)

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